All signals in the physical world are analog. Music, speech, images, movies, as well as wireless, fiber optic or wireline communication signals are continuous-time continuous-value signals. The core of the majority of electronic appliances use digital signal processing and memories, representing information with time and amplitude quantized signals. The analog-to-digital and digital-to-analog interfaces are crucial to reap the benefits of increasingly better digital signal processing. The number of analog-to-digital and digital-to-analog interfaces and their quality requirements has been increasing as semiconductor technology scaling has made the integration of whole electronic systems on a single chip possible.
Even though highly scaled CMOS technologies offer tremendous digital signal processing density and speed increases, the design of analog-to-digital and digital-to-analog interfaces becomes progressively harder with every new technology node. Although scaled technologies have resulted in higher clock frequencies, other analog characteristics of devices, such as DC gain and matching, have been deteriorating, and supply voltages have been shrinking substantially.
The progressive downscaling of the supply voltage as CMOS technologies scale is very challenging for analog circuits since reducing the supply voltage, reduces the maximum signal value and thus puts more demands on reducing noise or interference to maintain the same signal-to-noise ratio or dynamic range.
Accordingly, new circuits that can operate at lower supply voltages are desirable.